A320 NLG Snags

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StereoTechque
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Posts: 270
Joined: Sat Nov 28, 2015 7:24 am

A320 NLG Snags

Wed May 24, 2017 8:14 pm

Anybody aware what really was the cause behind this incident: :arrow: https://en.wikipedia.org/wiki/JetBlue_Flight_292

Wiki article says it was due failure of some o-rings in the Steering module. I have also heard that the BSCU performs certain steering checks on the NLG after deployed and before landing, and if they fail to respond per commands, the BSCU intenionally locks the NLG in the 90 degree position to prevent runway deviation after landing.

Also there have been instances where NLG have been accidently stowed on ground:
https://www.youtube.com/watch?v=BKGx4WBnskI

How can this happen even when the safety locks are not installed as there is a Baulk solenoid inside the Gear lever which prevents doing so on ground?
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HighBypass
Posts: 79
Joined: Mon May 22, 2017 3:03 am

Re: A320 NLG Snags

Wed May 24, 2017 10:58 pm

The nose wheel on the incident aircraft was found to have two of its four centering lugs fatigued - likely due (NTSB) to the system's repeated self-tests, by design, and under-engineering of the parts involved.

"The fatigue failure of two anti-rotation lugs due to repeated cyclic pre-landing tests, which allowed the nosewheels to deviate from the 0-degree position on landing gear retraction. A contributing factor was the design of the Brake Steering Control Unit (BSCU) system logic, which prevented the nosewheels from centering. Also contributing was the lack of a procedure to attempt to reset the BSCU system under these conditions."


Airbus has since redesigned parts of the nose wheel steering system, including a more robust linkage and reprogrammed the BSCU logic to enable an airborne reset of the BSCU. Increased inspection of the hydraulic cylinder bores, new seal replacement guidance, and improved linkages were also mandated via OEB since that incident.

Link to the full and final NTSB Report on the incident available here: https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20050927X01540&AKey=1&RType=Final&IType=IA
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StereoTechque
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Joined: Sat Nov 28, 2015 7:24 am

Re: A320 NLG Snags

Mon May 29, 2017 7:42 am

Thank you HighBypass. Your posts are really in depth and informative.
Any further information on the L/G stow on ground?
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HighBypass
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Re: A320 NLG Snags

Mon May 29, 2017 10:02 am

This is a great place to discuss and share information, and I have also benefitted. Thanks for the thanks StereoTechque!

I don't have knowledge of the other incident. Could be it wasn't mechanically locked, (damage or a malfunction: nose gear typically has an over-centering bar that stays in place) or perhaps engineers disabled not only the interlock but the air/ground system during some maintenance operation when hydraulics were pressurized. These are ways the feet can come out from under.
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